Your best bet is an entry-level DSLR (digital single-lens reflex) camera. Whether you choose Nikon, Canon, or Sony is really your call (they're all basically at the same level at the lower end), but I would suggest a Nikon or Canon kit to begin if you're planning on upgrading in the future; the second-tier manufacturers don't have the same amount of high quality equipment available when you want to upgrade.

I started out four years ago with a Canon T1i, an 18-55mm lens and a 55-250mm lens. The whole kit at the time cost a little under $800 USD and has suited me very well for spotting. You can probably find similar deals with the latest entry-level bodies today (the T4i and T5i from Canon). I would suggest taking a look at CNet's "Best Entry Level Digital SLR Cameras" article, it does a pretty good job of presenting the latest bodies available.

As for the lenses, again, I would start with the lower end lenses until you are confident that this hobby is something you want to invest in. The camera bodies will typically come with a "kit" lens, something along the lines of 18-55mm focal length. This type of lens will work well if you have close access to the aircraft, and will probably be enough for spotting large aircraft at Heathrow's Myrtle Ave, but you're going to want a little extra reach if you do much more than that. Both Canon and Nikon have a wide range of lenses in the 50ish-300ish range. Canon's 55-250mm is a bargain; the various 70-300mm lenses are very popular with spotters. Again, pick the lens which fits at your price range. In the most basic sense, the higher the focal length (the number in mms), the more "zoom" you get from the lens.

To echo the above, budget is everything. Looking to the future you can get photos on this site with kit lenses, e.g. 18-55 but you'll need to be close to the aircraft - just before landing for example, check the many photos in this link

Gear and location recommendations are great, but you would also do well to educate yourself about basic photography principles such as exposure and composition. It will help you when it is time to ask the inevitable question that I myself once asked, 'how come my pictures don't look like the ones here'

So as to not unduly influence any one educational resource, there are many books/videos/websites/workshops that do an excellent job teaching the basics. You should spend at LEAST as much time learning about photography as you do about gear.